Burglars generally try to avoid attracting attention with the sound of shattering glass, so by making windows difficult to pry open you'll discourage all but the most desperate crooks. As a further precaution, use outdoor motion-sensor spotlights to foil burglars who work at night.

Windows

Nails: Something as simple as a couple of nails will make it virtually impossible for an intruder to pry open traditional double-hung wood-framed windows. With a 5/32-inch bit, drill a set of holes at a slight downward angle all the way through each side of the lower window sash and halfway into the upper sash. Then slide a three-inch nail into each hole. To ensure that you can easily open windows, holes should be loose enough that the nails slide in and out smoothly.
To buy: Three-inch nails, a few cents each, available at hardware stores.
Installation time: 5 to 10 minutes per window.

Basement Windows

Security bars: Yes, the windows are small, but so are teenagers, who account for about 30 percent of burglary arrests annually. Mount custom-made 1-inch- or 1 1/2-inch-wide steel bars right into the window frame or, if your basement also serves as a bedroom or playroom (where a fire escape route is especially important), opt for adjustable quick-release bars.
To buy: For custom-made bars, check the Yellow Pages under "locksmiths" or "iron work." Ready-made quick-release Window Security Guards (two-pack), $63, www.acehardware.com.
Installation time: Varies.

Back of House

Motion-sensitive lights: Discourage nighttime prowlers by installing motion-sensitive lights. Putting up a Solar Masters Centurion solar-powered light won't even require an electrician's help — it gets all the power it needs from the sun and attaches to your home's exterior with the screws provided. A 12-foot cable lets you position the light and the solar panel in different locations for maximum sunlight.
To buy: Solar Masters Centurion, $90, www.solar-masters.com.
Installation time: 30 minutes per light.